1. esrevinU ehT

2. Goals:
give an overview of what we currently know about the cosmos and our place in it
What we know about space.
How we know it.
Kids are never the problem. They are born scientist. The problem is always the adults. They beat the curiosity out of the kids.

3. Where are we? We live on a planet… You are here
8000 miles
Earth is 92 million miles from the sun…

4. The solar system You are here The solar system: 1 star 9 main planets
many moons
5 dwarf planets
many small planets
1000s of asteroid rocks
Millions of comets
3 Billion miles
The sun is a star. It is 25 Trillion miles to the nearest other star.

5. Are there other solar systems out there?
Yes!
We now know of 100s of known planets around other stars
We mostly detect them through their gravitational effects on their stars
Although a few we can image directly
Most that we can detect are huge and close to their star
In the next ~20 years, we will detect planets that are more like Earth

6. The Milky Way galaxy There are ~400 Billion stars in our galaxy
You are here
5.7x1017 miles
= 5.7 million trillion miles

7. There are ~100 Billion galaxies
You are here
So we belong to one of 10 billion stars in our galaxy, and there are 100 billion galaxies…
4x1021 miles

8. But that’s only a small part of the story…
Everything we know about and everything we have ever seen (stars, planets, interstellar matter, intergalactic matter, and all of the light and radiation out there), is only 4% of what makes up the universe!
Ordinary
Matter
(You are here)
3.2% free H and He gas
0.3% neutrinos
0.5% stars and big planets
0.005% heavy elements
(you are here)

9. Has it always been this way?no
The universe is ~14 billion years old
At the start, everything was in a very dense state, and it has been expanding since
The expansion is now accelerating

10. A brief history
t=0 Big Bang – beginning of universe
Major milestones:
10-8 seconds: “inflation” makes universe blow up in size
10-6 seconds: Quarks combine to form protons and neutrons
300,000 years: Neutral hydrogen forms
400 million years: Matter collapses to form first stars
400 million years thru present: the elements are formed by stellar fusion and explosions
1 billion years thru present: Galaxies and super-galactic structures form
~4 billion years ago: Sun and planets coalesce from dust ejected from earlier stars
~2.5 billion years ago: Life appears on Earth
~1 billion years ago: Multicellular life appears
~750 million years ago: First animals
~100 million years ago: First mammals
~1 million years ago: First humans
~5000 years ago: First human civilizations

11. Question 1: Which is the farthest from the Earth? The sun Neptune
The center of our galaxy
The Andromeda galaxy

12. Question 2:
Approximately how many times more dark matter is there than ordinary matter in the Universe? 2 5 20 50
Ordinary
Matter

13. Question 3:
The Earth has been around for approximately what fraction of the time history of the Universe?
1/10
1/3
1/2
2/3
Universe: 14 billion years old
Earth: 4.5 billion years old

14. How do we know all this?
- We study the light that comes to us from distant objects
- We investigate the laws of physics here on Earth and believe they apply everywhere
- We get some particles (electrons, protons, neutrons, neutrinos, etc…) from celestial objects

15. Step 1: Telescopes
Our eyes are small and don’t collect much light, so only very bright astronomical objects are visible to the naked eye.
Also astronomical objects are far away so they appear very small and can’t be resolved in detail by the eye.
Telescopes solve both problems: they gather the light falling on a much larger area than the eye, focus it to a small area, then magnify it. The resulting image is then viewed or recorded.
Hubble space telescope, present
Galileo uses telescope to look at Jupiter, 1609
LSST is one of a new generation of huge telescopes, 2015

16. Telescopes First people looked with their eyes and drew what they saw
Galileo’s drawing of the Moon
Then they recorded images with photographic film
Actual photograph from ~1900
Now we record images digitally - like with your digital camera -and store them as data
Hubble Space Telescope image

17. Step 2: Spectra
We can also split up the light from an object that we get with a telescope into the different colors (wavelengths) and record them individually
This spectroscopy gives us extra useful information…

18. Spectra
Spectroscopy allows us to see the brightness as a function of color (wavelength).
Increasing wavelength
This often yields lots of information. For example, we can see the presence (or absence) of different atoms and compounds that emit light at specific wavelengths

19. Spectra
Not only that, but we can see the spectrum ‘shift’ for some objects.
This shift in wavelength is caused by the motion of the source relative to us. It is analogous to the change in pitch of a car horn when the car moves.

20. Spectra
When the car is coming toward us, the waves in front are compressed, decreasing the wavelength:
When the car is moving away us, the waves in back are elongated, increasing the wavelength:
The same thing happens for light.

21. Spectra we can see the spectrum ‘shift’ for some objects.
Analyzing the shift tells us how the object is moving!

22. Telescopes
Ok, we can record the light from objects, and even split it into different colors.
Some are bright and some are dim.
They have different color patterns
Some are moving
How far are they?

23. Step 3: Distances
Something may appear bright or faint because it actually is bright or faint or because it is close to us or far away
We need to measure distances
The distances to very nearby stars can be determined by measuring angles in a technique known as “parallax”

24. Distances Farther distances rely on “standard candles”
From nearby objects whose distance is known via parallax we can determine that certain types have an intrinsic brightness (“luminosity”).
For farther objects of the same type, since we know how bright they actually are, and we see how bright they appear, we can determine the distance

25. Question 4:
Relative to a source that is stationary with respect to us, a source moving away from us has its sound (and light) wavelengths:
The same
longer
shorter

26. Put it all together!
Now that we have all of these stars and galaxies, and their distances, and their sizes, and how they are moving, we can start to build a clearer picture of the universe
We can put all of the stars, galaxies, and everything else that we see where it all belongs.
That’s what people have been doing for 100s of years, and continue to do
There have been and continue to be surprises though…

27. Discovery: Expansion of the universe and big bang
Armed with a way to measure the distance to other galaxies, Hubble did so, and also took the galaxies’ spectra (1929).
He saw a shift in the spectral lines
The spectral lines from the more distant galaxies were shifted toward the red (longer wavelength), indicating that those galaxies were moving away from us

28. Expansion of the universe
We define the redshift (z) to quantify how much the light is shifted in wavelength toward the red
Hubble showed that there was a relation between distance and redshift. The farther a galaxy is from us, the more it is redshifted and therefore the faster it is moving away.
Three major conclusions:
1) Since the farther something is the longer it takes for light to reach us, higher redshift is equivalent to saying farther back in time
2) If across the board, the farther away something is the faster it is receding, then the only conclusion is that the entire universe as whole is expanding.
3) Run the movie backwards and the Universe must have started with everything in a very small volume and has expanded since – the “big bang”

29. Step 4: There’s more light out there than meets the eye…
Visible light is only a small piece of the available light out there
Increasing frequency
Different processes in space produce emission all over the spectrum!
microwave

30. All the different kinds of light
Different processes in space produce emission all over the spectrum!
Over the past 100 years, we have developed detectors – the equivalent of optical telescopes, for all of these different kinds of light.
FERMI LAT

31. Question 5:
Which of the following is not the name of a range of wavelengths of light?
visible
X-rays
ultra-luminous
microwave
radio
microwave

32. The different light tells us so much
For example, looking at the center of our own galaxy:
Fast electrons and magnetic field
Cold gas
Dust
Stars unobscured
Stars
Hot gas
Cosmic rays (charged particles)

33. Contents of galaxies Galaxies consist of: Stars (and planets) Cold gas
Hot gas
“Dust” (heavy elements and molecules)
Free cosmic rays (electrons, protons, neutrons, neutrinos)
Dark matter (!)
The space between Galaxies in clusters consists of very hot gas, and in empty space consists of free electrons and protons
And it all glows (in different parts of the spectrum) so we see it
But it turns out there is MUCH MORE out there…

34. Discovery: Exotic objects
There is a slew of crazy stuff out there, characterized by systematically studying the sky on many different scales at many different wavelengths.
Many stars are in closely orbiting binary or many-star systems
Supernovae are huge explosions when a massive star dies. Most of the elements that make up the Earth and us were fused in supernovae.
Pulsars are rapidly rotating neutron stars (very dense supernova remnants) that send out beams of radio energy

35. Central black holes
The big black holes at the centers of Galaxies (including ours) are a million or more times as massive as the sun
Active Galactic Nuclei are matter orbiting a massive black hole at the center of a galaxy. They sometimes send out huge jets of very fast particles.
The jets of particles slam into the neighboring gas and magnetic fields and radiate x-rays, UV, optical, and radio
Because they are so bright, we can see some of them at a great distance. Those are called Quasars

36. Active Galactic Nuclei
If the jet is pointed right at us, it looks like a really bright, flaring point, and we call it a “Blazar”
If the jet is pointed perpendicular to us, we can sometimes see the jets shooting way out. The far lobes make a “Radio Galaxy”

37. An AGN – the “Death Star” Galaxy
“Death Star” galaxy (x-ray, radio, and optical)
Another galaxy
jet
Galaxy with AGN
X-rays – purple
Optical – red
Radio - blue

38. GRBs
Gamma ray bursts may happen when a neutron star falls into another neutron star or black hole.
The resulting explosion sends out particles and radiation all over the spectrum
They are the most luminous things in the universe
In May a GRB was seen at redshift 8. It is the farthest thing ever seen and occurred only 400 million years after the big bang

39. Cosmic Microwave Background
Observing the sky at microwave wavelengths, we can even see light almost back to the big bang:
A glow covers the entire sky, light from a time when the early universe was hot and dense. It lends additional proof to the big bang explaination.
Those hotter and colder patches in the hot and dense sea tell us a lot. They are the seeds of what will become structure.

40. Discovery: Dark Matter
Galaxies and groups of galaxies behave like they have a lot more matter than just adding up the stars, gas, and dust
1) Galaxy rotation: We can measure (via spectral line shift) the velocities of stars in Galaxies. The bulk rotation rate of the galaxies is related to how much matter is in them, and there seems to be way more matter than we can see

41. Dark Matter
Galaxies and clusters behave like they have a lot more matter than just adding up the things we can see: stars, gas, and dust
1) Galaxy rotation
2) Galaxy cluster dynamics: The motion of galaxies within groups of galaxies also indicates there is much more matter there (first claimed by Fritz Zwicky in 1933!)

42. Dark Matter
Galaxies and clusters behave like they have a lot more matter than just adding up the things we can see: stars, gas, and dust
1) Galaxy rotation
2) Galaxy cluster dynamics
3) Gravitational Lensing: Matter can bend light. The amount of light bending we see for objects behind galaxies and galaxy clusters indicates a lot of unseen matter in the clusters.

43. Dark Matter
Galaxies and clusters behave like they have a lot more matter than just adding up the things we can see: stars, gas, and dust
1) Galaxy rotation
2) Galaxy cluster dynamics
3) Gravitational Lensing
4) Colliding galaxy clusters: check out the picture
Lensing says the mass is here
So the majority of the matter passed right through each other without interacting, and it doesn’t give off light.
2 clusters passed through each other:
X-ray observations say the gas (ordinary matter) is here. The gas from the two clusters collided and stayed in the middle

44. Dark Matter
Galaxies and clusters behave like they have a lot more matter than just adding up the things we can see: stars, gas, and dust
1) Galaxy rotation
2) Galaxy cluster dynamics
3) Gravitational Lensing
4) Colliding galaxy clusters
5) Patterns in the CMB

45. Dark Matter
Galaxies and clusters behave like they have a lot more matter than just adding up the things we can see: stars, gas, and dust
1) Galaxy rotation
2) Galaxy cluster dynamics
3) Gravitational Lensing
4) Colliding galaxy clusters
5) Patterns in the CMB
Dark matter interacts gravitationally, but we know that it doesn’t give off light (at any wavelength) and that it mostly passes right through itself.
Hence “Dark”
Dark matter is ~80% of the matter in the universe.
The ordinary matter is only 20%
We don’t know what it is (although there are theories).

46. Dark Matter Dark matter is ~80% of the matter in the universe.
The ordinary matter is only 20%
The large scale structure of the Universe consists of vast ‘filaments’ of dark matter in which the galaxies and clusters sit at the vertices of the web
Galaxies and clusters sit in ‘halos’ of dark matter.
The dark matter can’t be as clumped like ordinary matter because it can’t radiate energy or angular momentum, so it stays ‘swimming’ in large structures

47. Discovery: Dark Energy
Question 1: how is the expansion of the universe evolving with time? Is it steady, or has it slowed down or sped up?
Question 2: What is the total energy content?
According to Einstein’s General Relativity, Energy can be in the form of:
Matter
Light
“Vacuum energy” – pushes things apart
The answers to these two questions are related, because the energy content controls the expansion
By quantifying how distances change with time (or equivalently, redshift) we can determine the expansion history and shape, and answer both questions

48. Dark Energy
Until recently, we didn’t have a method for determining very large distances, only those to relatively nearby galaxies
In the 90s, people determined that a certain type of supernova (Ia) could be used as a standard candle
in the late 90s they were able to determine the actual distance to high redshift (z>1) galaxies and found a surprising result…
The relationship between distance and redshift (time) shows that:
The expansion of the universe is now accelerating with time!

49. Dark Energy
Meanwhile, observations of the tiny differences (anisotropy) in the CMB show the primordial seeds of structure in the early universe.
We have theories that relate the size of those seeds to what we see today, and they depend on the energy content…
Adding up all the ordinary matter and dark matter leaves us with 75% of the energy missing!

50. Dark Energy Accelerating expansion + missing energy
 some sort of vacuum energy is present
“Dark energy”
We have no idea what it is or where it comes from.
But it’s large, and it’s (apparently) in charge
Supernova Ia, CMB, and cluster evolution all agree: ~70% Dark Energy, ~30% Matter

51. Dark Energy
Also, knowing the expansion history, we can relate redshift to distance accurately.
Knowing the speed of light, once we have the distance we can calculate the time it took for light from something to get here.
We know the redshift of the CMB. We can get the distance, and then the time it took for the light from the CMB to get here. That is almost the age of the universe
age of the universe  13.7 billion years

52. Question 8:
Which of the following is not a source of evidence for Dark Energy?
supernova as standard candles to determine far distances
patterns of small variation in the CMB
galaxy rotation measurements

53. “ΛCDM” Cosmology
All of this leads to the standard so called concordance cosmology, or “ΛCDM” (Lambda stands for vacuum energy and ‘CDM’ is “cold dark matter”).
The universe started from a very dense state 13.7 Billion years ago and has
expanded ever since
In the very beginning the expansion was enormous (inflation). The expansion
then resumed a lower value
The gravitational formation of large scale structure is dominated by dark matter
Ordinary matter forms the stars, galaxies, and intergalactic gas. It is what we see.
As the universe expands and the matter density drops, dark energy is increasingly
taking over and causing the expansion to accelerate
At present, the universe is 70% Dark Energy,
~25% Dark Matter, and ~5% Baryons

54. Outstanding Questions in cosmology
What is dark matter?
What is dark energy? Does it evolve with time?
What is the fate of the universe?
Why did the universe start in the first place? What caused the big bang?
Is there life out there?
Are there other universes?
What happens in a black hole?
Many others !